Through her research at the University of Pennsylvania — and firsthand experience teaching in New York City's public schools —psychologist Angela Duckworth has found that the ability to withstand stress and move past failures to achieve a goal is the best indicator of future success.

"What struck me was that IQ was not the only difference between my best and my worst students," she shared in her recent TED talk. "Some of my strongest performers did not have stratospheric IQ scores. Some of my smartest kids weren't doing so well."

After teaching in New York City, Duckworth went to graduate school to become a psychologist, where she studied what types of people were successful at West Point Military Academy, the National Spelling Bee, in classrooms, and beyond. Again, she said, "it wasn't social intelligence. It wasn't good looks, physical health, and it wasn't IQ. It was grit."

She began by studying gritin the Chicago public schools. "I asked thousands of high school juniorsto take grit questionnaires,and then waited around more than a yearto see who would graduate," she said. "Turns out that grittier kidswere significantly more likely to graduate,even when I matched them on every characteristic I could measure,things like family income,standardized achievement test scores,even how safe kids felt when they were at school."

In a paper, "Self-Discipline Outdoes IQ In Predicting Academic Performance Of Adolescents," Duckworth and colleague Martin Seligman tested 164 eighth graders "recruited from a socioeconomically and ethnically diverse magnet public school" in the Northeast for self-discipline and IQ. They measured the students in the fall and spring through self-assessment, a behavioral delay-of-gratification task, and a survey of study and lifestyle habits, along with a group IQ test. They found that "self-discipline predicted academic performance more robustly than did IQ. Self-discipline also predicted which students would improve their grades over the course of the school year, whereas IQ did not."

But why do some people have grit and others don't? That's where science needs to fill in the gaps.

"What I do know is that talent doesn't make you gritty," Duckworth said in her TED talk. "Our data show very clearly that there are many talented individuals who simply do not follow through on their commitments. In fact, in our data, grit is usually unrelated or even inversely related to measures of talent."

One way to instill it, she says, it to help people understand that learning and ability isn't fixed. And that there's life after failure.